Field of the Invention
This invention relates to organophotoreceptors suitable for use in electrophotography and, more specifically, to flexible organophotoreceptors having novel charge transport compounds.
Background of the Art
In electrophotography, an organophotoreceptor in the form of a plate, disk, sheet, belt, or drum having an electrically insulating photoconductive element on an electrically conductive substrate is imaged by first uniformly electrostatically charging the surface of the photoconductive layer, and then exposing the charged surface to a pattern of light. The light exposure selectively dissipates the charge in the illuminated areas, thereby forming a pattern of charged and uncharged areas. A liquid or solid toner is then deposited in either the charged or uncharged areas to create a toned image on the surface of the photoconductive layer. The resulting visible toner image can be transferred to a suitable receiving surface such as paper. The imaging process can be repeated many times.
Both single layer and multilayer photoconductive elements have been used. In the single layer embodiment, a charge transport material and charge generating material are combined with a polymeric binder and then deposited on the electrically conductive substrate. In the multilayer embodiment, the charge transport material and charge generating material are in the form of separate layers, each of which can optionally be combined with a polymeric binder, deposited on the electrically conductive substrate. Two arrangements are possible. In one arrangement (the xe2x80x9cdual layerxe2x80x9d arrangement), the charge generating layer is deposited on the electrically conductive substrate and the charge transport layer is deposited on top of the charge generating layer. In an alternate arrangement (the xe2x80x9cinverted dual layerxe2x80x9d arrangement), the order of the charge transport layer and charge generating layer is reversed.
In both the single and multilayer photoconductive elements, the purpose of the charge generating material is to generate charge carriers (i.e., holes or electrons) upon exposure to light. The purpose of the charge transport material is to accept these charge carriers and transport them through the charge transport layer in order to discharge a surface charge on the photoconductive element.
To produce high quality images, particularly after multiple cycles, it is desirable for the charge transport material to form a homogeneous solution with the polymeric binder and remain in solution. In addition, it is desirable to maximize the amount of charge which the charge transport material can accept (indicated by a parameter known as the acceptance voltage or xe2x80x9cVaccxe2x80x9d), and to minimize retention of that charge upon discharge (indicated by a parameter known as the residual voltage or xe2x80x9cVresxe2x80x9d).
There are many charge transport materials available for electrophotography. The most common charge transport materials are pyrazoline derivatives, fluorene derivatives, oxadiazole derivatives, stilbene derivatives, hydrazone derivatives, carbazole hydrazone derivatives, polyvinyl carbazole, polyvinyl pyrene, or polyacenaphthylene. However, each of the above charge transport materials suffer some disadvantages. There is always a need for novel charge transport materials to meet the various requirements of electrophotography applications.
A charge transport compound having the following generic formula:
(Rxe2x80x94Q)n-Yxe2x80x83xe2x80x83Formula I
wherein R is a heterocyclic group, preferably a heterocyclic group selected from the group consisting of julolidine ring groups, carbazole ring groups, and triarylmethane ring groups (examples of other heterocyclic groups being the following non-limiting list of such as thiazoline, thiazolidine, phenothiazine, oxazoline, imidazoline, imidazolidine, thiazole, oxazole, isoxazole, oxazolidinone, morpholine, imidazole, benzothiazole, benzotriazole, benzoxazole, benzimidazole, naphthothiazole, naphthoxazole, naphthimidazole, quinoline (e.g., 2-quinoline or 4-quinoline), isoquinoline, quinoxaline, indole, indazole, pyrrole, purine, pyrrolidine, pyridine, piperidine, pyridazine, pyrazoline, pyrimidine, pyrazine, triazole, oxadiazole, tetrazole, urazole, carbazole, julolidine, or thiadiazole ring.);
Q comprises an aromatic hydrazone linking group, such as 
Y comprises a bridging group between Rxe2x80x94Qxe2x80x94 groups, such as a bond, carbon atom, nitrogen atom, oxygen atom, sulfur atom, a branched or linear xe2x80x94(CH2)pxe2x80x94 group where p is an integer between 0 and 10, an aryl group, a cycloalkyl group, a cyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a heterocyclic group, or a CR10 group where R10 is hydrogen atom, an alkyl group, or aryl group;
Z is an aryl group, preferably a phenyl group or naphthyl group;
X is a linking group, preferably a methylene group, and for example having the formula xe2x80x94(CH2)mxe2x80x94 (branched or linear), where m is an integer between 0 and 20, inclusive, and one or more of the methylene groups is optionally replaced by an oxygen atom, a carbonyl group, urethane, urea, an ester group, a xe2x80x94NR6 group, a CHR7 group, or a CR8R9 group where R6, R7, R8, and R9 are, independently, H, an alkyl group, or aryl group; and
n is an integer between 2 and 6, inclusive.
In another aspect of the invention, the invention features an organic photoreceptor that includes:
(a) a charge transport compound having the formula
(Rxe2x80x94Q)n-Yxe2x80x83xe2x80x83Formula I
wherein R is a heterocyclic group, preferably a heterocyclic group selected from the group consisting of julolidine ring groups, carbazole ring groups, and triarylmethane ring groups (examples of other heterocyclic groups being the following non-limiting list of such as thiazoline, thiazolidine, phenothiazine, oxazoline, imidazoline, imidazolidine, thiazole, oxazole, isoxazole, oxazolidinone, morpholine, imidazole, benzothiazole, benzotriazole, benzoxazole, benzimidazole, naphthothiazole, naphthoxazole, naphthimidazole, quinoline (e.g., 2-quinoline or 4-quinoline), isoquinoline, quinoxaline, indole, indazole, pyrrole, purine, pyrrolidine, pyridine, piperidine, pyridazine, pyrazoline, pyrimidine, pyrazine, triazole, oxadiazole, tetrazole, urazole, carbazole, julolidine, or thiadiazole ring.);
Q comprises an aromatic hydrazone linking group, such as 
Y comprises a bridging group, preferably a divalent linking group, between Rxe2x80x94Qxe2x80x94 groups, such as a bond, carbon atom, nitrogen atom, oxygen atom, sulfur atom, a branched or linear xe2x80x94(CH2)pxe2x80x94 group where p is an integer between 0 and 10, an aryl group, a cycloalkyl group, a cyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a heterocyclic group, or a CR10 group where R10 is hydrogen atom, an alkyl group, or aryl group;
Z is an aryl group, preferably a phenyl group or naphthyl group;
X is a linking group, preferably a methylene group, and for example having the formula xe2x80x94(CH2)mxe2x80x94 (branched or linear), where m is an integer between 0 and 20, inclusive, and one or more of the methylene groups is optionally replaced by an oxygen atom, a carbonyl group, urethane, urea, an ester group, a xe2x80x94NR6 group, a CHR7 group, or a CR8R9 group where R6, R7, R8, and R9 are, independently, H, an alkyl group, or aryl group; and
n is an integer between 2 and 6, inclusive;
(b) a charge generating compound; and
(c) an electrically conductive substrate.
A charge transport compound having the following generic formula:
(Rxe2x80x94Q)n-Yxe2x80x83xe2x80x83Formula I
wherein R is a heterocyclic group, preferably a heterocyclic group selected from the group consisting of julolidine ring groups, carbazole ring groups, and triarylmethane ring groups (examples of other heterocyclic groups being the following non-limiting list of such as thiazoline, thiazolidine, phenothiazine, oxazoline, imidazoline, imidazolidine, thiazole, oxazole, isoxazole, oxazolidinone, morpholine, imidazole, benzothiazole, benzotriazole, benzoxazole, benzimidazole, naphthothiazole, naphthoxazole, naphthimidazole, quinoline (e.g., 2-quinoline or 4-quinoline), isoquinoline, quinoxaline, indole, indazole, pyrrole, purine, pyrrolidine, pyridine, piperidine, pyridazine, pyrazoline, pyrimidine, pyrazine, triazole, oxadiazole, tetrazole, urazole, carbazole, julolidine, or thiadiazole ring.);
Q comprises an aromatic hydrazone linking group, such as 
Y comprises a bridging group between Rxe2x80x94Qxe2x80x94 groups, such as a bond, carbon atom, nitrogen atom, oxygen atom, sulfur atom, a branched or linear xe2x80x94(CH2)pxe2x80x94 group where p is an integer between 0 and 10, an aryl group, a cycloalkyl group, a cyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a heterocyclic group, or a CR10 group where R10 is hydrogen atom, an alkyl group, or aryl group;
Z is an aryl group, preferably a phenyl group or naphthyl group;
X is a linking group, preferably a methylene group, and for example having the formula xe2x80x94(CH2)mxe2x80x94 (branched or linear), where m is an integer between 0 and 20, inclusive, and one or more of the methylene groups is optionally replaced by an oxygen atom, a carbonyl group, urethane, urea, an ester group, a xe2x80x94NR6 group, a CHR7 group, or a CR8R9 group where R6, R7, R8, and R9 are, independently, H, an alkyl group, or aryl group; and
n is an integer between 2 and 6, inclusive.
Various specific classes of charge transport compound within the scope of Formula I include, but are not limited to the following:
In a first aspect, the invention features an organophotoreceptor that includes:
(a) a charge transport compound having the formula 
where n is an integer between 2 and 6, inclusive;
R1, R2, R3, and R4 are, independently, hydrogen, a halogen atom, hydroxy group, thiol group, an alkoxy group, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, nitro group, an amino group, a cycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., a phenyl or naphthyl group); and
X is a linking group having the formula xe2x80x94(CH2)mxe2x80x94, branched or linear, where m is an integer between 0 and 50, inclusive, and one or more of the methylene groups is optionally replaced by a bond, an oxygen atom, a sulfur atom, a carbonyl group, an urethane group, an urea group, an ester group, an aryl group, a cycloalkyl group, a cyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a heterocyclic group, a NR5 group, a CHR6 group, or a CR7R8 group where R5, R6, R7, and R8 are, independently, H, an alkyl group, or an aryl group.
The charge transport compound may or may not be symmetrical. Thus, for example, a linking group X for any given xe2x80x9carmxe2x80x9d of the compound may be the same or different from the linking groups in other xe2x80x9carmsxe2x80x9d of the compound. Similarly, the R1, R2, R3, and R4 groups for any given xe2x80x9carmxe2x80x9d of the compound may be the same or different from the R1, R2, R3, and R4 groups in any other arm. In addition, the above-described formula for the charge transport compound is intended to cover isomers; or
b) a charge transport compound of the formula: 
where n is an integer between 2 and 6, inclusive;
R1 is hydrogen, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, or an aryl group (e.g., a phenyl or naphthyl group);
R2 is hydrogen, a halogen, hydroxy group, thiol group, an alkoxy group, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, a cycloalkyl group (e.g. a cyclohexyl group), an aryl group (e.g., a phenyl or naphthyl group), or a xe2x80x94NR4R5 group where R4 and R5 are, independently, hydrogen, a branched or linear alkyl group, a branched or linear unsaturated hydrocarbon group, a cycloalkyl group, an aryl group, or R4 and R5 combine with the nitrogen atom to form a ring;
R3 is hydrogen, a halogen, hydroxy group, thiol group, an alkoxy group, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, a cycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., a phenyl or naphthyl group);
X is a linking group having the formula xe2x80x94(CH2)mxe2x80x94, branched or linear, where m is an integer between 0 and 20, inclusive, and one or more of the methylene groups is optionally replaced by an oxygen atom, a carbonyl group, urethane, urea, an ester group, a xe2x80x94NR6 group, a CHR7 group, or a CR8 R9 group where R6, R7, R8, and R9 are, independently, H, an alkyl group, or aryl group; and
Y is a bond, carbon atom, nitrogen atom, oxygen atom, sulfur atom, a branched or linear xe2x80x94(CH2)pxe2x80x94 group where p is an integer between 0 and 10, an aryl group, a cycloalkyl group, a cyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a heterocyclic group, or a CR10 group where R10 is hydrogen atom, an alkyl group, or aryl group;
(b) a charge generating compound; and
(c) an electrically conductive substrate.
The charge transport compound may or may not be symmetrical. Thus, for example, a linking group X for any given xe2x80x9carmxe2x80x9d of the compound may be the same or different from the linking groups in other xe2x80x9carmsxe2x80x9d of the compound. Similarly, the R1, R2, and R3 groups for any given xe2x80x9carmxe2x80x9d of the compound may be the same or different from the R1, R2, and R3 groups in any other arm. In addition, the above-described formula for the charge transport compound is intended to cover isomers.
The organic photoreceptor may be provided in the form of a flexible belt. In one embodiment, the organic photoreceptor includes: (a) a charge transport layer comprising the charge transport compound and a polymeric binder; (b) a charge generating layer comprising the charge generating compound and a polymeric binder; and (c) the electrically conductive substrate. The charge transport layer may be intermediate the charge generating layer and the electrically conductive substrate. Alternatively, the charge generating layer may be intermediate the charge transport layer and the electrically conductive substrate.
The invention also features the charge transport compounds themselves. In one preferred embodiment, a charge transport compound is selected in which n is 2, Y is a bond or a xe2x80x94CH2xe2x80x94 group, X has the formula xe2x80x94CH2)mxe2x80x94 where m is an integer between 2 and 5, inclusive, and R1 is an ethyl, heptyl, or xe2x80x94(CH2)3C6H5 group. Specific examples of suitable charge transport compounds have the following formulae: 
In one preferred embodiment, a charge transport compound is selected in which n is 2, X is a (CH2)m group where m is an integer between 2 and 20, and R1, R2, R3, and R4 are hydrogen. Specific examples of suitable charge transport compound have the following general formula where m is an integer between 2 and 20; more preferably m is an integer between 4 and 10; most preferably m is 5, as in Compound (11). 
In a second aspect, the invention features an electrophotographic imaging apparatus that includes (a) a plurality of support rollers, at least one having a diameter no greater than about 40 mm; and (b) the above-described organic photoreceptor in the form of a flexible belt threaded around the support rollers. The apparatus preferably further includes a liquid toner dispenser.
In a third aspect, the invention features an electrophotographic imaging process that includes (a) applying an electrical charge to a surface of the above-described organic photoreceptor; (b) imagewise exposing the surface of the organic photoreceptor to radiation to dissipate charge in selected areas and thereby form a pattern of charged and uncharged areas on the surface; (c) contacting the surface with a liquid toner that includes a dispersion of colorant particles in an organic liquid to create a toned image; and (d) transferring the toned image to a substrate.
In a fourth aspect, the invention features a novel charge transport material having the formula 
where n is an integer between 2 and 6, inclusive;
R1 is hydrogen, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, or an aryl group (e.g., a phenyl or naphthyl group);
R2 is hydrogen, a halogen, hydroxy group, thiol group, an alkoxy group, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, a cycloalkyl group (e.g. a cyclohexyl group), an aryl group (e.g., a phenyl or naphthyl group), or a xe2x80x94NR4R5 group where R4 and R5 are, independently, hydrogen, a branched or linear alkyl group, a branched or linear unsaturated hydrocarbon group, a cycloalkyl group, an aryl group, or R4 and R5 combine with the nitrogen atom to form a ring;
R3 is hydrogen, a halogen, hydroxy group, thiol group, an alkoxy group, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, a cycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., a phenyl or naphthyl group);
X is a linking group having the formula xe2x80x94(CH2)mxe2x80x94, branched or linear, where m is an integer between 0 and 20, inclusive, and one or more of the methylene groups is optionally replaced by an oxygen atom, a carbonyl group, urethane, urea, an ester group, a xe2x80x94NR6 group, a CHR7 group, or a CR8R9 group where R6, R7, R8, and R9 are, independently, H, an alkyl group, or aryl group; and
Y is a bond, carbon atom, nitrogen atom, oxygen atom, sulfur atom, a branched or linear xe2x80x94(CH2)pxe2x80x94 group where p is an integer between 0 and 10, an aryl group, a cycloalkyl group, a cyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a heterocyclic group, or a CR10 group where R10 is hydrogen atom, an alkyl group, or aryl group.
Mixed (e.g., at least two Q groups are selected from two different classes selected from the group consisting of julolidine, carbazole, and triarylmethane) may be represented by the following various subgeneric formulae: 
Specific subgeneric examples of charge transport compound according to formula (IV) have the following general formula (V) where m is an integer between 2 and 20; more preferably m is an integer between 4 and 10. 
Another example of such a mixed charge transport compound has the formula (VI): 
where R1 is hydrogen, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, a cycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., a phenyl or naphthyl group);
R2, R3, R4, R5, and R6 are, independently, hydrogen, a halogen atom, hydroxy group, thiol group, an alkoxy group, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, nitro group, an amino group, a cycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., a phenyl or naphthyl group); and
X is a linking group having the formula xe2x80x94(CH2)mxe2x80x94, branched or linear, where m is an integer between 0 and 50, inclusive, and one or more of the methylene (CH2) groups is optionally replaced by oxygen atom, sulfur atom, a carbonyl group, an urethane group, an urea group, an ester group, an aryl group, a heterocyclic group, a cycloalkyl group, a cyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a cycloalkyl group, a cyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a NR7 group, a CHR8 group, or a CR8R10 group where R7, R8, R9, and R10, are, independently, H, an alkyl group, or an aryl group.
In one specific embodiment of structural Formula VI, a charge transport compound is selected in which X is a xe2x80x94CH2)mxe2x80x94 group where m is an integer between 2 and 20, R1 is an alkyl group, and R2, R3, R4, R5 and R6 are hydrogen. Specific examples of suitable charge transport compound have the following general formula where m is an integer between 2 and 20; more preferably m is an integer between 4 and 10. 
and Formula (IX) wherein:
the subgeneric formula below applies: 
where R1 is hydrogen, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, a cycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., a phenyl or naphthyl group);
R2, R3, R4, R5, and R6 are, independently, hydrogen, a halogen atom, hydroxy group, thiol group, an alkoxy group, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, nitro group, an amino group, a cycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., a phenyl or naphthyl group); and
X is a linking group having the formula xe2x80x94(CH2)mxe2x80x94, branched or linear, where m is an integer between 0 and 50, inclusive, and one or more of the methylene (CH2) groups is optionally replaced by oxygen atom, sulfur atom, a carbonyl group, an urethane group, an urea group, an ester group, an aryl group, a heterocyclic group, a cycloalkyl group, a cyclosiloxyl group (e.g., a cyclotetrasiloxyl group), a NR7 group, a CHR8 group, or a CR9R10 group where R7, R8, R9, and R10, are, independently, H, an alkyl group, or an aryl group.
Another generic formula (IX) is directed to charge transport compounds having the formula 
wherein R1 and R2 are, independently, hydrogen, a halogen atom, hydroxy group, thiol group, an alkoxy group, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, nitro group, an amino group, a cycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., a phenyl or naphthyl group);
X is a linking group having the formula xe2x80x94(CH2)mxe2x80x94, branched or linear, where m is an integer between 0 and 50, inclusive, and one or more of the methylene groups is optionally replaced by a bond, an oxygen atom, a sulfur atom, a carbonyl group, an urethane group, an urea group, an ester group, an aryl group, a heterocyclic group, a NR4 group, a CHR5 group, or a CR6 R7 group where R4, R5, R6, and R7 are, independently, H, an alkyl group, or an aryl group; and
Y and Z are, independently, a carbazole group, a triphenylamine group, a julolidine group, or any of their derivatives.
The charge transport compound may have more than two arms such that the linking group X may be linked to more than two hydrazone groups. The charge transport compound may or may not be symmetrical. Thus, for example, a portion of the linking group X attached to any given xe2x80x9carmxe2x80x9d of the compound may be the same or different from the remaining portion of the linking groups attached to other xe2x80x9carmsxe2x80x9d of the compound. Similarly, the R1 and R2 groups may be the same or different and the Y and Z groups may be the same or different. In addition, the above-described formula for the charge transport compound is intended to cover isomers.
Another subgeneric formula (XI) for this class of charge transport compound with only triarylmethane Q substituents has the formula 
where n is an integer between 2 and 6, inclusive;
R1, R2, and R3 are, independently, hydrogen, a halogen atom, hydroxy group, thiol group, an alkoxy group, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, an ether group, nitro group, an amino group, a cycloalkyl group (e.g. a cyclohexyl group), or an aryl group (e.g., a phenyl or naphthyl group); and
X is a linking group having the formula xe2x80x94(CH2)mxe2x80x94, branched or linear, where m is an integer between 0 and 50, inclusive, and one or more of the methylene groups is optionally replaced by a bond, an oxygen atom, a sulfur atom, a carbonyl group, an urethane group, an urea group, an ester group, an aryl group, a heterocyclic group, a NR4 group, a CHR5 group, or a CR6R7 group where R4, R5, R6, and R7 are, independently, H, an alkyl group, or an aryl group. Specific and subgeneric central nucleus examples of this formula (XI) are represented by: 
Another aspect of the invention is the formation of charge transport compounds with at least three hydrazone moieties or groups attached to the bridging group. These compounds are represented by the general formula, falling within generic Formula I, of a charge transport compound having the formula: 
R1, R2, and R3 are, independently, a branched or linear alkyl group (e.g., a C1-C20 alkyl group), a branched or linear unsaturated hydrocarbon group, a cycloalkyl group (e.g. a cyclohexyl group), a heterocyclic group, or an aryl group (e.g., a phenyl or naphthyl group);
R4, R5, and R6 are, independently, triarylamine (e.g., triphenylamine), diaryl alkylamine, dialkyl arylamine, a carbocyclic ring such as anthraquinone, diphenoquinone, indane, or fluorenone, or a heterocyclic ring such as thiazoline, thiazolidine, phenothiazine, oxazoline, imidazoline, imidazolidine, thiazole, oxazole, isoxazole, oxazolidinone, morpholine, imidazole, benzothiazole, benzotriazole, benzoxazole, benzimidazole, naphthothiazole, naphthoxazole, naphthimidazole, quinoline (e.g., 2-quinoline or 4-quinoline), isoquinoline, quinoxaline, indole, indazole, pyrrole, purine, pyrrolidine, pyridine, piperidine, pyridazine, pyrazoline, pyrimidine, pyrazine, triazole, oxadiazole, tetrazole, urazole, carbazole, julolidine, or thiadiazole ring. These heterocyclic rings may also have substituents such as halogen atoms (e.g., chlorine, bromine and fluorine), alkyls (e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl, t-octyl, octyl, octadecyl, etc.), alkoxys (e.g., methoxy, ethoxy, butoxy, etc.), aryls (e.g., phenyl, tolyl, xylyl, etc.), aryloxys (e.g., phenoxy, methylphenoxy, chlorophenoxy, dimethylphenoxy, etc.), N-substituted aminos (e.g., N-methylamino, N-ethylamino, N-t-butylamino, N-octylamino, N-benzylamino, acetylamino, benzoylamino, etc.), N,N-disubstituted aminos (e.g., N,N-dimethylamino, N,N-diethylamino, N,N-dipropylamino, N,N-di-t-butylamino, N,N-dibenzylamino, N-ethyl-N-benzylamino, etc.), acyls (e.g., acetyl, propionyl, benzoyl, methylbenzoyl, dimethylbenzoyl, chlorobenzoyl, etc.), carbamoyl, sulfamoyl, nitro, cyano, hydroxy, carboxy, sulfonate, oxo, benzo, naptho, indeno, and phosphate; and
X is a linking group having the formula 
where m, n, and o is an integer between 0 and 50, inclusive; one or more of the methylene groups is optionally replaced by a bond, an oxygen atom, a sulfur atom, a carbonyl group, an urethane group, an urea group, an ester group, an aryl group, a heterocyclic group, a NR5 group, a CHR6 group, or a CR7R8 group where R5, R6, R7, and R8 are, independently, H, an alkyl group, or an aryl group; and the C-H group is optionally replaced by a nitrogen atom, a boron atom, a metal atom, and a CR9 group where R9 is an alkyl group or an aryl group.
A photoconductor system exits with a combination of a) and (b) a charge generating compound; and (c) an electrically conductive substrate.
The charge transport compound may have more than three arms such that the linking group X may be linked to more than three hydrazone groups. The charge transport compound may or may not be symmetrical. Thus, for example, a portion of the linking group X attached to any given xe2x80x9carmxe2x80x9d of the compound may be the same or different from the remaining portion of the linking groups attached to other xe2x80x9carmsxe2x80x9d of the compound. Similarly, the R1, R2, and R3 groups may be the same or different and the R4, R5, and R6 groups may be the same or different. In addition, the above-described formula for the charge transport compound is intended to cover isomers.
The organophotoreceptor may be provided in the form of a plate, a disc, a flexible belt, a rigid drum, or a sheet around a rigid or compliant drum. In one embodiment, the organophotoreceptor includes: (a) a charge transport layer comprising the charge transport compound and a polymeric binder; (b) a charge generating layer comprising the charge generating compound and a polymeric binder; and (c) the electrically conductive substrate. The charge transport layer may be intermediate between the charge generating layer and the electrically conductive substrate. Alternatively, the charge generating layer may be intermediate between the charge transport layer and the electrically conductive substrate.
In describing chemicals by structural formulae and group definitions, certain terms are used in a nomenclature format that is chemically acceptable. The terms groups, central nucleus, and moiety have defined meanings. The term group indicates that the generically recited chemical material (e.g., alkyl group, phenyl group, carbazole group, etc.) may have any substituent thereon which is consistent with the bond structure of that group. For example, alkyl group includes alkyl materials such as methyl ethyl, propyl iso-octyl, dodecyl and the like, and also includes such substituted alkyls such as chloromethyl, dibromoethyl, 1,3-dicyanopropyl, 1,3,5-trihydroxyhexyl, 1,3,5-trifluorocyclohexyl, 1-methoxy-dodecyl, and the like. However, as is consistent with such nomenclature, no substitution would be included within the term that would alter the fundamental bond structure of the underlying group. For example, where a pheny ring group or central nucleus of a phenyl group is recited, substitution such as 1-hydroxyphenyl, 2,4-fluorophenyl, orthocyanophenyl, 1,3,5-trimethoxyphenyl and the like would be acceotable within the terminology, while substitution of 1,1,2,2,3,3-hexamethylphenyl would not be acceptable as that substitution would require the ring bond structure of the phenyl group to be altered to a non-aromatic form because of the substitution. Similarly, where the term a xe2x80x9ccentral nucleus of the formulaxe2x80x9d is used and a structural formula is shown, any substituent may be provided on that formula, as long as the substutution does not alter the underlying bond structure of the formula (e.g., by require a double bond to be converted to a single bond, or opening a ring group, or dropping a described substituent group in the formula). Where the term moirty is used, such as alkyl moiety or phenyl moiety, that terminology indicates that the chemical material is not substituted.
In a second aspect, the invention features an electrophotographic imaging apparatus that includes (a) a plurality of support rollers; and (b) the above-described organophotoreceptor in the form of a flexible belt threaded around the support rollers. The apparatus preferably further includes a liquid toner dispenser.
In a third aspect, the invention features an electrophotographic imaging process that includes (a) applying an electrical charge to a surface of the above-described organophotoreceptor; (b) imagewise exposing the surface of the organophotoreceptor to radiation to dissipate charge in selected areas and thereby form a pattern of charged and uncharged areas on the surface; (c) contacting the surface with a liquid toner that includes a dispersion of colorant particles in an organic liquid to create a toned image; and (d) transferring the toned image to a substrate.
In a fourth aspect, the invention features a novel charge transport material having the formula 
R1, R2, and R3 are, independently, described above;
R4, R5, and R6 are, independently, as described above;
X is a linking group having the formula 
where m, n, and o are as described above.
Specific examples of suitable charge transport compounds have the following formulae: 
The charge transport compounds according to Formulae (I)-(XIII) may be prepared by a multi-step synthesis using a combination of known synthetic techniques.
The first step is the preparation of one or more of aldehyde derivative of any heterocyclic compound, preferably carbazole, triphenylamine, or julolidine (heterocyclic group, preferably a heterocyclic group selected from the group consisting of julolidine ring groups, carbazole ring groups, and triarylmethane ring groups (examples of other heterocyclic groups being the following non-limiting list of such as thiazoline, thiazolidine, phenothiazine, oxazoline, imidazoline, imidazolidine, thiazole, oxazole, isoxazole, oxazolidinone, morpholine, imidazole, benzothiazole, benzotriazole, benzoxazole, benzimidazole, naphthothiazole, naphthoxazole, naphthimidazole, quinoline (e.g., 2-quinoline or 4-quinoline), isoquinoline, quinoxaline, indole, indazole, pyrrole, purine, pyrrolidine, pyridine, piperidine, pyridazine, pyrazoline, pyrimidine, pyrazine, triazole, oxadiazole, tetrazole, urazole, carbazole, julolidine, or thiadiazole ring) by Vilsmeier reaction between carbazole, triphenylamine, or julolidine correspondingly and phosphorus oxychloride (POCl3). Carbazole, triphenylamine, or julolidine is dissolved in N,N-dimethylformamide (DMF) and then the solution is cooled. Then POCl3 (10-15% excess) is added slowly via a dropping funnel to the cooled DMF solution.
The second step is the reaction between phenylhydrazine and one of the aldehyde derivative of carbazole, triphenylamine, or julolidine in a molar ratio of 1:1 to form the corresponding hydrazone derivative by refluxing the reactants in THF for two hours. More than one hydrazone derivative may be prepared if an unsymmetrical charge transport compound is desired.
The last step is the reaction of one of the hydrazone with a dibromoalkane in a molar ratio of 2:1 to form a symmetrical charge transport compound. The hydrazone obtained is dissolved in DMSO. After the addition of 25% aqueous solution of NaOH, a dibromoalkane is added to the solution. This solution is stirred at 70xc2x0 C. for approximately 1 hour. The product from this reaction is purified by recrystallization. If an unsymmetrical charge transport compound is desired, two or more different hydrazones are used. Each hydrazone will react, one at a time, with a dibromoalkane or an alkane with more than two bromo groups in a molar ratio of 1:1 under condition described above.
Formula 12 may be prepared by the condensation reaction of 4-(diphenylamino)-benzaldehyde with phenyl hydrazine; and then by a nucleophilic substitution reaction of the product of the condensation reaction with a dibromoalkane to form the final dimeric charge transport material. Specifically, Compound 13 may be prepared according to the above synthesis wherein the dibromoalkane is 1,5-dibromopentane.
The invention provides novel charge transport materials for organic photoreceptors featuring a combination of good mechanical and electrostatic properties. These photoreceptors can be used successfully with liquid toners to produce high quality images. The high quality of the images is maintained after repeated cycling.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.
The invention features organic photoreceptors that include charge transport compounds having the formulae set forth in the Summary of the Invention above. The charge transport compounds according to Formula (1) may be prepared by a multi-step synthesis using a combination of known synthetic techniques. For example, the general synthetic method for synthesis of Compounds 5-7 was according to a 4-step synthetic procedure. The first step is N-alkylatation of carbazole to introduce an alkyl group to the carbazole nitrogen. The second step is the formation of a xe2x80x94CHO group on the carbazole ring by Vilsmeier reaction. The third step is the formation of hydrazone by the reaction of the product from step 2 with a hydrazine. The last step is a nucleophilic substitution reaction to form a bridging group between two or more hydrazone moieties. Compounds 2-4 were prepared according to the above procedure except the first and second steps were skipped because the starting materials for step three are commercially available.
The organophotoreceptor may be in the form of a plate, drum, or belt, with flexible belts being preferred. The organophotoreceptor may include an electrically conductive substrate and a photoconductive element in the form of a single layer that includes both the charge transport compound and charge generating compound in a polymeric binder. Preferably, however, the organophotoreceptor includes an electrically conductive substrate and a photoconductive element that is a bilayer construction featuring a charge generating layer and a separate charge transport layer. The charge generating layer may be located intermediate the electrically conductive substrate and the charge transport layer. Alternatively, the photoconductive element may be an inverted construction in which the charge transport layer is intermediate the electrically conductive substrate and the charge generating layer.
The electrically conductive substrate may be flexible, for example in the form of a flexible web or a belt, or inflexible, for example in the form of a drum. Typically, a flexible electrically conductive substrate comprises of an insulated substrate and a thin layer of electrically conductive materials. The insulated substrate may be paper or a film forming polymer such as polyethylene terepthalate, polyimide, polysulfone, polyethylene naphthalate, polypropylene, nylon, polyester, polycarbonate, polyvinyl fluoride, polystyrene and the like. Specific examples of supporting substrates included polyethersulfone (Stabar S-100, available from ICI), polyvinyl fluoride (Tedlar, available from E.I. DuPont de Nemours and Company), polybisphenol-A polycarbonate (Makrofol, available from Mobay Chemical Company) and amorphous polyethylene terephthalate (Melinar, available from ICI Americas, Inc.). The electrically conductive materials may be graphite, dispersed carbon black, iodide, conductive polymers such as polypyroles and Calgon Conductive polymer 261 (commercially available from Calgon Corporation, Inc., Pittsburgh, Pa.), metals such as aluminum, titanium, chromium, brass, gold, copper, palladium, nickel, or stainless steel, or metal oxide such as tin oxide or indium oxide. Preferably, the electrically conductive material is aluminum. Typically, the photoconductor substrate will have a thickness adequate to provide the required mechanical stability. For example, flexible web substrates generally have a thickness from about 0.01 to about 1 mm, while drum substrates generally have a thickness of from about 0.5 mm to about 2 mm. Typical structures for polycarbonates include: 
The charge generating compound is a material which is capable of absorbing light to generate charge carriers, such as a dyestuff or pigment. Examples of suitable charge generating compounds include metal-free phthalocyanines (e.g., Progen 1 x-form metal-free phthalocyanine from Zeneca, Inc.), metal phthalocyanines such as titanium phthalocyanine, copper phthalocyanine, oxytitanium phthalocyanine, hydroxygallium phthalocyanine, squarylium dyes and pigments, hydroxy-substituted squarylium pigments, perylimides, polynuclear quinones available from Allied Chemical Corporation under the tradename Indofast Double Scarlet, Indofast Violet Lake B, Indofast Brilliant Scarlet and Indofast Orange, quinacridones available from DuPont under the tradename Monastral Red, Monastral Violet and Monastral Red Y, naphthalene 1,4,5,8-tetracarboxylic acid derived pigments including the perinones, tetrabenzoporphyrins and tetranaphthaloporphyrins, indigo- and thioindigo dyes, benzothioxanthene-derivatives, perylene 3,4,9,10-tetracarboxylic acid derived pigments, polyazo-pigments including bisazo-, trisazo- and tetrakisazo-pigments, polymethine dyes, dyes containing quinazoline groups, tertiary amines, amorphous selenium, selenium alloys such as selenium-tellurium, selenium-tellurium-arsenic and selenium-arsenic, cadmium sulphoselenide, cadmiumselenide, cadmium sulphide, and mixtures thereof. Preferably, the charge generating compound is oxytitanium phthalocyanine, hydroxygallium phthalocyanine or a combination thereof.
Preferably, the charge generation layer comprises a binder in an amount of from about 10 to about 90 weight percent and more preferably in an amount of from about 20 to about 75 weight percent, based on the weight of the charge generation layer.
The binder is capable of dispersing or dissolving the charge transport compound (in the case of the charge transport layer) and the charge generating compound (in the case of the charge generating layer). Examples of suitable binders for both the charge generating layer and charge transport layer include polystyrene-co-butadiene, modified acrylic polymers, polyvinyl acetate, styrene-alkyd resins, soya-alkyl resins, polyvinylchloride, polyvinylidene chloride, polyacrylonitrile, polycarbonates, polyacrylic acid, polyacrylates, polymethacrylates, styrene polymers, polyvinyl butyral, alkyd resins, polyamides, polyurethanes, polyesters, polysulfones, polyethers, polyketones, phenoxy resins, epoxy resins, silicone resins, polysiloxanes, poly(hydroxyether) resins, polyhydroxystyrene resins, novolak, poly(phenylglycidyl ether)-co-dicyclopentadiene, copolymers of monomers used in the above-mentioned polymers, and combinations thereof. Polycarbonate binders are particularly preferred. Examples of suitable polycarbonate binders include polycarbonate A which is derived from bisphenol-A, polycarbonate Z, which is derived from cyclohexylidene bisphenol, polycarbonate C, which is derived from methylbisphenol A, and polyestercarbonates.
The photoreceptor may include additional layers as well. Such layers are well-known and include, for example, barrier layers, release layers, adhesive layer, and sub-layer. The release layer forms the uppermost layer of the photoconductor element with the barrier layer sandwiched between the release layer and the photoconductive element. The adhesive layer locates and improves the adhesion between the barrier layer and the release layer. The sub-layer is a charge blocking layer and locates between the electrically conductive substrate and the photoconductive element. The sub-layer may also improve the adhesion between the electrically conductive substrate and the photoconductive element.
Suitable barrier layers include coatings such as crosslinkable siloxanol-colloidal silica coating and hydroxylated silsesquioxane-colloidal silica coating, and organic binders such as polyvinyl alcohol, methyl vinyl ether/maleic anhydride copolymer, casein, polyvinyl pyrrolidone, polyacrylic acid, gelatin, starch, polyurethanes, polyimides, polyesters, polyamides, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, polycarbonates, polyninyl butyral, polyvinyl acetoacetal, polyvinyl formal, polyacrylonitrile, polymethyl methacrylate, polyacrylates, polyvinyl carbazoles, copolymers of monomers used in the above-mentioned polymers, vinyl chloride/vinyl acetate/vinyl alcohol terpolymers, vinyl chloride/vinyl acetate/maleic acid terpolymers, ethylene/vinyl acetate copolymers, vinyl chloride/vinylidene chloride copolymers, cellulose polymers, and mixtures thereof. The above organic binders optionally may contain small inorganic particles such as fumed silica, silica, titania, alumina, zirconia, or a combination thereof. The typical particle size is in the range of 0.001 to 0.5 micrometers, preferably 0.005 micrometers. A preferred barrier layer is a 1:1 mixture of methyl cellulose and methyl vinyl ether/maleic anhydride copolymer with glyoxal as a crosslinker.
The release layer topcoat may comprise any release layer composition known in the art. Preferably, the release layer is a fluorinated polymer, siloxane polymer, fluorosilicone polymer, silane, polyethylene, polypropylene, or a combination thereof. More preferably, the release layers is crosslinked silicone polymers.
Typical adhesive layers include film forming polymers such as polyester, polyvinylbutyral, polyvinylpyrolidone, polyurethane, polymethyl methacrylate, poly(hydroxy amino ether) and the like. Preferably, the adhesive layer is poly(hydroxy amino ether). If such layers are utilized, they preferably have a dry thickness between about 0.01 micrometer and about 5 micrometers.
Typical sub-layers include polyvinylbutyral, organosilanes, hydrolyzable silanes, epoxy resins, polyesters, polyamides, polyurethanes, silicones and the like. Preferably, the sub-layer has a dry thickness between about 20 Angstroms and about 2,000 Angstroms.
The charge transport compounds, and photoreceptors including these compounds, are suitable for use in an imaging process with either dry or liquid toner development. Liquid toner development is generally preferred because it offers the advantages of providing higher resolution images and requiring lower energy for image fixing compared to dry toners. Examples of useful liquid toners are well-known. They typically include a colorant, a resin binder, a charge director, and a carrier liquid. A preferred resin to pigment ratio is 2:1 to 10:1, more preferably 4:1 to 8:1. Typically, the colorant, resin, and the charge director form the toner particles.
The invention will now be described further by way of the following examples.